1. Technical Field
A data input/output buffer that can exactly sense an input signal even if the signal is inputted as a low voltage due to a drop in a threshold voltage, and a semiconductor memory device using the same are disclosed.
2. Discussion of Related Art
A semiconductor device is provided with a buffer for retaining a given inputted signal even if the input of the signal is stopped after the signal is inputted. Of these buffers, there is a page buffer or a data output buffer that is used for an NAND type flash memory device.
In an NAND type flash memory device constructed in a string unit, data stored at cells are buffered in the page buffer upon a read operation. Furthermore, data stored at a page buffer of a number of page buffers, which is selected by a column multiplexer, are transferred to a data line via the data output buffer.
As such, the buffer functions to temporarily retain the data signal. At this time, there is no problem when the data signal is inputted as a Low level, but there may be a problem when the data signal is inputted as a High level. For example, if the data signal passes through a switching element such as a logical element or a transistor, a voltage of the data signal is lowered as much as a threshold voltage. If the voltage of the data signal is lowered as such, the transfer rate of the signal is lowered. Due to this, not only the operating speed of the circuit is lowered, but also the buffer cannot exactly sense whether the data signal is a High level or a Low level. This causes a serious problem that the circuit operates at low voltage.